Inkjet printers operate a plurality of inkjets in each printhead to eject liquid ink onto an image receiving member. The ink can be stored in reservoirs that are located within cartridges installed in the printer. Such ink can be aqueous ink or an ink emulsion. Other inkjet printers receive ink in a solid form and then melt the solid ink to produce liquid ink for ejection onto the imaging member. The printer supplies ink to printheads for ejection through inkjets onto an image receiving surface of an image receiving member, such as a print medium or an indirect imaging belt or imaging drum. Liquid inks dry and phase change inks cool into a solid state after being transferred to a print medium, such as paper or any other suitable medium for printing.
A typical inkjet printer uses one or more printheads with each printhead containing an array of individual nozzles through which drops of ink are ejected by inkjets across an open gap to an image receiving member to form an ink image. The image receiving member can be a continuous web of recording media, a series of media sheets, or the image receiving member can be an indirect image receiving member, such as a print drum or endless belt. Images printed on indirect image receiving members are later transferred to recording media by mechanical force in a transfix nip formed by the rotating surface and a transfix roller.
In an inkjet printhead, individual piezoelectric or electrostatic actuators generate mechanical forces that expel ink through an aperture, usually called a nozzle, in a faceplate of the printhead. The actuators expel an ink drop in response to an electrical signal, sometimes called a firing signal, activating an actuator. The amplitude, or voltage level, of the firing signals affects the amount of ink ejected in an ink drop. The firing signal is generated by a printhead controller with reference to image data. A print engine in an inkjet printer processes the image data to identify the inkjets in the printheads of the printer that must be operated to eject a pattern of ink drops at particular locations on the image receiving member to form an ink image corresponding to the image data.
In order for the printed images to correspond closely to the image data, both in terms of fidelity to the image objects and the colors represented by the image data, the printheads are registered with reference to the imaging surface and with the other printheads in the printer. In a printer with multiple printheads, the individual inkjets within each printhead are registered with reference to each other and the printheads are registered with reference to each other to enable the printer to form printed images using one or more colors of ink from multiple printheads. In a single printhead, a process direction registration process adjusts the time at which different inkjets eject ink drops to enable the printhead to eject the ink drops onto predetermined locations of an image receiving surface to form, for example, continuous lines that extend in the cross-process direction with a series of ink drops that are substantially collinear to each other.
While the existing solutions for drop placement adjustment correct for some drop placement errors, the existing solutions often lack precision in registration between multiple inkjets in a printhead. For example, existing registration processes use time adjustment corrections that modify the operation of the inkjet by time increments that correspond to an integer size of the printed drops on the image receiving surface. The registration errors between inkjets often include non-integer or fractional errors that cannot be fully corrected by existing registration processes. Consequently, improvements to registration processes for inkjets in printers that enable registration between inkjets that have fractional drop size errors would be beneficial.